In order to determine the level of bacteriological and physicochemical pollution delivered to the Gulf of Montijo by San Pedro River, samples were collected from the mouth of the river outlet. The area did not show pollution as to certain physicochemical parameters studied (TSS, pH, BOD, OD). However, there are warnings signs about detergent concentrations detected during the months of April and May (0.95 mg/dm3) in most sampling stations. Similarly, there is concern on the nutrient concentrations detected, especially nitrates in the rainy season, which average concentrations ranged between 1.084 mg/dm3 and 2.444 mg/dm3. The findings of fecal coliforms in all sampling sites suggest the presence of human feces and / or animals, which can be downloaded directly or indirectly into the river.